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[Display omitted] • Fe/NC catalyst shows good activity and stability for cleaving C-O bonds in lignite. • Fe-N and Fe/Fe 3 C species in the catalyst were crucial to the catalytic activity. • Active hydrogen species were hydrogen radicals generated from H 2 and isopropanol. • The hydrocracking products have higher H/C ratio and heating values than lignite. • Catalytic hydrocracking promoted producing phenols via the cleavage of C-O bonds. Cleaving C-O bridged bonds of lignite via catalytic hydrocracking (CHC) is an effective method to produce chemicals and clean fuels. Herein, a nitrogen-doped carbon supported Fe catalyst was developed by using a one-pot method for CHC of Xilinguole lignite (XL) and its related model compounds. The doped nitrogen enhanced the interaction between Fe and N species to form Fe-N sites and favored forming smaller Fe/Fe 3 C nanocrystals, which played a crucial role in CHC performance. Toluene and phenol were produced from CHC of benzyl phenyl ether (BPE) with high yield and selectivity at 250 °C over the optimal catalyst with 4% Fe, without hydrogenation products. The Fe-based catalyst activated both H 2 and isopropanol to generate hydrogen radicals for cleaving C-O bridged bonds. The CHC of XL under different temperature and time showed that the yields of oil, asphaltene and preasphaltene were obviously promoted under 325 °C, 1 MPa, and 6 h, and they had much higher H/C ratio but remarkably lower O/C ratio, resulting in much higher heating values (28.19–36.90 MJ/kg) than XL. Phenols were the major group component with relative content of 53.6 wt% in oil from CHC, and the asphaltene and preasphaltene from CHC had obviously lower molecular weights, which could attributed to depolymerization of C-O bridged bonds in the XL macromolecular structures over the catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective hydrogenolysis of diphenyl ether C-O bond occurred over Ni/Nb 2 O 5. • The common hydrogen supply existed between H 2 and isopropanol. • Hydrodeoxygenation reaction hardly occurred due to the weak acidity of Ni/Nb 2 O 5. • The reaction route of the hydrogenolysis in DPE was presented. Selective cleavage of stable ether C-O bonds is particularly of significance for the valorization of lignin and designing high active and cheap catalysts attracts researchers to conduct a lot of investigations. The niobium species containing both Brønsted and Lewis acid sites can be applied in hydrodeoxygenation of diphenyl ether (DPE). It is important to regulate the acidity of niobium to achieve the selective cleavage of DPE without hydrodeoxygenation. Herein, the weakly acidic Ni/Nb 2 O 5 prepared by an incipient wetness impregnation method could efficiently cleave C-O bonds of DPE without hydrodeoxygenation. DPE was completely converted and the yields of target products (cyclohexane and cyclohexanol) reached 90% under the coexistence of H 2 and isopropanol. It was ascribed to the common hydrogen supply between H 2 and isopropanol which could produce more active hydrogen. Acetone was detected in the solution after the reaction, demonstrating that a dehydrogenation reaction of isopropanol provided hydrogen. In addition, the turnover frequency (TOF) and the apparent activation energy (E a) for catalytic hydrogenolysis of DPE revealed that Ni/Nb 2 O 5 possessed higher activity than Co/Nb 2 O 5 under the same conditions. The possible reaction pathways were also summarized and analyzed. [ABSTRACT FROM AUTHOR]

• Ru/AC exhibited high activity and selectivity for cleaving of C-O bond in BPE. • The turnover frequency and activation energies of Ru catalysts were calculated. • The different H sources (H 2 and solvent) in hydrogenolysis reaction were compared. • The hydrogenolysis route under different H-donor conditions was presented. Selective hydrogenolysis, the aromatic ether C-O bonds under mild conditions, is crucial for the valorization of lignin. In this context, the effects of H 2 and solvent on the hydrogenolysis of lignin model compounds over Ru catalysts were explored. With H 2 as hydrogen donor, the Ru/AC exhibited the highest activity for converting lignin model compounds into monomeric compounds, whereas H 2 led to low selectivity of aromatics. However, isopropanol was the good H-donor solvent, which could provide a large amount of active hydrogen to promote the cleavage of C-O bonds. Additionally, the yield of aromatics in isopropanol was higher than that under H 2 atmosphere. It could be ascribed to the fact that isopropanol is the protic solvent which displays Lewis basicity, and is a good H-bond donor and a good H-bond acceptor. The higher electron-releasing inductive effect of isopropanol made it easier to provide active hydrogen. Based on the experiments, the mechanism of benzyl phenyl ether hydrogenolysis in H 2 and isopropanol system was presented. [ABSTRACT FROM AUTHOR]

• Selective hydrogenation of aromatic rings in lignin model compounds over Ru/Nb 2 O 5. • H 2 rather than solvents provided the only hydrogen source in this reaction. • Hydrodeoxygenation reaction did not occur due to the acid loss of Ru/Nb 2 O 5. • The reaction route of the aromatic rings hydrogenation in DPE was presented. Selective aromatic ring hydrogenation is an important process for the valorization of lignin and designing the high active and selective catalyst is still a challenge. At present, it is reported that such catalysts generally have some shortcomings including strict reaction conditions, complicated catalyst preparation and low reaction efficiency. Herein, Ru/Nb 2 O 5 catalyst with the macropore structure prepared by an incipient wetness impregnation method could effectively promote the aromatic rings hydrogenation of various lignin-derived compounds under extremely mild condition (30 °C). The resulting aliphatic compounds with the high yield provided abundant raw materials for the production of fine chemicals and biofuels. In this case, further experiments revealed that it was H 2 rather than solvents provided the only hydrogen source. A relatively low bond energy of Ru0 in Ru/Nb 2 O 5 promoted the formation of active hydrogen from H 2. Due to the acid loss of Ru/Nb 2 O 5 catalyst, the hydrodeoxygenation reaction did not occur. Moreover, the catalyst was investigated under different influence parameters in order to obtain the optimal reaction conditions (30 °C, 3 MPa H 2). The application of Ru/Nb 2 O 5 catalyst may provide a promising approach to the value-added utilization of lignin-derived fragments. [ABSTRACT FROM AUTHOR]